1. Field of the Invention
The present invention relates to an image reading apparatus and an image forming apparatus.
2. Description of Related Art
Conventionally, there have been known image reading apparatuses which are provided to digital copiers, printers, facsimile machines and such like, the reading apparatuses including auto document feeders (hereinafter, referred to as ADFs) for conveying documents to image reading sections (scanner sections) in the image reading apparatuses.
One of the methods for reading images by the image reading apparatuses which include the above ADFs is a method of fixing an image reading section at a predetermined position below a platen glass which is included in the image reading apparatus and moving the documents one by one at a constant speed above the image reading section to read the images.
By adopting the above reading method, the burden of setting a document on a platen glass is resolved and the time required for replacing documents can be shortened. Thus, processing can be performed to a large amount of documents rapidly, and operability and productivity can be largely improved.
Many users of the image reading apparatuses use binders and document filing folders when filing documents. An appropriate sheet size is determined for each of the binders and document filing folders. When a sheet which is larger than the sheet size by one size is to be filed together with the sheets of the sheet size, the sheet is Z-folded in some cases so as to conform to the sheet size. That is, the document bundle has only the documents of standard size having no folded parts (hereinafter, referred to as non-folded documents) in some cases, and the document bundle includes Z-folded documents and such like which are Z-folded and mixed in the non-folded documents in other cases. The Z-folded document indicates a document which is folded back at the middle position in the long direction so that the front surface overlaps itself, and further folded back at the middle position in the long direction of the folded part so that the back surface overlaps itself. When a document is Z-folded, the size thereof in the long direction is half of the size before the document is folded. Thus, the sheet size of the document is reduced by one size. For example, when an A3 size document is Z-folded, the folded document is A4 size. When a B4 size document is Z-folded, the folded document is B5 size. Accordingly, by Z-folding a document, it is possible to match the sheet size of the document to the non-folded document which is smaller than the document by one size.
In a case where the documents are Z-fold mixed documents which include Z-folded documents (for example, A3 documents) mixed in non-folded documents (for example, A4 documents), when a document size, is detected on the document tray, there is a problem that the document size is detected as A4 document (non-Z-folded documents) though the documents include A3 documents (Z-folded documents).
As a technique for resolving the above problem, there is disclosed a technique of detecting the length of document during conveyance of document and correcting the reading position on the basis of the detected document length (for example, see Japanese Patent Application Laid Open Publication No. 2002-182320). According to the technique described in Japanese Patent Application Laid Open Publication No. 2002-182320, image reading of the Z-fold mixed documents can be performed accurately.
However, as for the memory management of image data of the read images, the management size of image data is set in advance by the document size as a reference which was detected on the document tray before the reading is started. In a case where the image data is data for a Z-folded document, the management size needs to be changed to the size which is larger by one size. Accordingly, system control needs to be changed according to temporary stop of reading operation and change of reading speed, thus lowering productivity according to the reading. Furthermore, though there is a method of detecting the document size for each image reading and performing memory management on the basis of the detected information, time is required for every time detection of document size and setting of management size in this case, thus still lowering productivity according to the reading. The above technique described in Japanese Patent Application Laid Open Publication No. 2002-182320 cannot resolve the above problem according to image data after reading though image reading of Z-fold mixed documents can be performed accurately.
Though there is a method of setting the management size on the basis of the maximum readable document size as a reference (for example, document size of Z-folded document), the method has had a problem that, when image data of non-Z-folded document is stored, wasted space is generated in the page memory and the memory management is not efficient.